Subdiffusion and its causes in both in vivo and in vitro lipid membranes have become the focus of recent research. We report apparent subdiffusion, observed via single particle tracking (SPT), in a homogeneous system that only allows normal diffusion (a DMPC monolayer in the fluid state). The apparent subdiffusion arises from slight errors in finding the actual particle position due to noise inherent in all experimental SPT systems. A model is presented that corrects this artifact, and predicts the time scales after which the effect becomes negligible. The techniques and results presented in this paper should be of use in all SPT experiments studying normal and anomalous diffusion.

The present study was undertaken to determine whether y-aminobutyric acid in the paraventricular nucleus contributes to the regulation of cardiovascular function. Blood pressure and heart rate were recorded and plasma catecholamines were measured in conscious rats receiving microinfusions of either artificial cerebrospinal fluid or a y-aminobutyric acid antagonist, bicuculline methiodide, bilaterally into the paraventricular nucleus. Artificial cerebrospinal fluid had no effect on any of the recorded variables. In contrast, infusion of bicuculline into the region of the paraventricular nucleus produced increases in blood pressure (20 ±2 mm Hg), heart rate (110±ll beats/min), and plasma concentrations of norepinephrine (640±107 pg/ml) and epinephrine (l t 266±267 pg/ml). Pretreatment with a ganglionic blocking agent abolished both the blood pressure (-1±2 mm Hg) and heart rate (5±18 beats/min) effects. Bilateral adrenal medullectomy reduced the changes in plasma norepinephrine concentrations (81 ±14 pg/ml) significantly and abolished the changes in plasma epinephrine concentrations (5±4 pg/ml). Conversely, adrenal medullectomy reduced the pressor effects (18±2 mm Hg) only slightly while the heart rate responses were attenuated (42 ±9 beats/min) by approximately 50%. These results suggest that an endogenous y-aminobutyric acid system exerts a tonic inhibitory effect on the sympathetic nervous system at the level of the paraventricular nucleus of the hypothalamus. (Hypertension 1991;18:48-55) A growing body of evidence suggests that -y-aminobutyric acid (GABA) plays an important role in central cardiovascular control. Intracerebroventricular injections of GABA agonists produced decreases in arterial pressure, heart rate, and peripheral sympathetic nerve activity. 1 -5 Conversely, intracerebroventricular administration of GABA antagonists, such as bicuculline methiodide (BMI) or picrotoxin, resulted in marked increases in blood pressure and heart rate due to an increase in sympathetic nervous system activity. 6 -8 In addition, alterations in GABA function have been implicated in the pathogenesis of hypertension.7 ' 9 - 14It has been proposed that a forebrain periventricular GABA system exerts a tonic inhibitory influence over the sympathetic nervous system. 4 At present, the available evidence suggests that this GABAergic site is located within the hypothalamus. 1516 A number of regions within the hypothalamus contain relatively high concentrations of GABA, including the anterior Received July 6,1990; accepted in revised form March 13, 1991. hypothalamic area, the posterior hypothalamic area, and the paraventricular nucleus (PVN) of the hypothalamus. 1718 Recent studies suggest that GABA exerts a tonic depressor effect within the posterior hypothalamic region.19 -22 On the other hand, the PVN has been suggested as a site of integration for autonomic and endocrine cardiovascular responses. 23 Neuroanatomic and electrophysiological data have indicated that the PVN is reciprocally connected to other areas of th...

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Everyday social interaction is often dominated by categorical thinking, with generic group-based knowledge structures guiding people's dealings with others. Noting the important influence that category-cueing facial features exert during the initial stages of person construal, the current work explored the effects of hair cues on the process and temporal dynamics of sex categorization. Using a standard priming paradigm to index the products of person construal (i.e., categorical and stereotypebased knowledge), the results of three experiments revealed that: (i) hair cues alone are sufficient to trigger category and stereotype activation; and (ii) during the early stages of person perception, these cues have the capacity to reverse conventional priming effects and generate errors of categorical assignment (e.g., female faces prime male knowledge). These findings are considered in the context of contemporary accounts of person construal.

Animals with bilateral cannulas in the paraventricular nucleus were made hypertensive by a one-kidney, figure eight renal wrap procedure or sham operated. Femoral artery and vein catheters were inserted for arterial pressure measurement and plasma catecholamine determination. After recovery and 4 days after hypertension surgery, bicuculline methiodide or muscimol was microinjected into the paraventricular nucleus. In some rats, nitroprusside was infused intravenously to reflexly stimulate the sympathetic nervous system. In control rats, bicuculline increased blood pressure, heart rate, and plasma norepinephrine and epinephrine concentrations. In contrast, in hypertensive rats blood pressure did not change while the heart rate response was maintained. Plasma norepinephrine and epinephrine responses were reduced 75 and 68%, respectively. Muscimol injections decreased arterial pressure in the hypertensive rats. Heart rate responses to nitroprusside were similar in the two groups of rats, while the plasma catecholamine responses were attenuated in the hypertensive animals. These data suggest that GABA function in the paraventricular nucleus is reduced in renal wrap hypertension.

All people share knowledge of cultural stereotypes of social groups--but what are the origins of these stereotypes? We examined whether stereotypes form spontaneously as information is repeatedly passed from person to person. As information about novel social targets was passed down a chain of individuals, what initially began as a set of random associations evolved into a system that was simplified and categorically structured. Over time, novel stereotypes emerged that not only were increasingly learnable but also allowed generalizations to be made about previously unseen social targets. By illuminating how cognitive and social factors influence how stereotypes form and change, these findings show how stereotypes might naturally evolve or be manipulated.

The present study was undertaken to determine the hemodynamic responses associated with stimulation of the hypothalamic paraventricular nucleus (PVN). Male Sprague-Dawley rats (n = 21) were instrumented with guide cannulas directed bilaterally at the PVN, with an electromagnetic flow probe placed on the ascending aorta and with femoral venous and arterial catheters. Bicuculline methiodide (BMI, 2 mM) was infused bilaterally (100 nl/20 min) into the PVN region before and after treatment with the beta 1-adrenergic antagonist, metoprolol bitartrate (2 mg/kg iv) or the alpha 1-adrenergic receptor antagonist, prazosin hydrochloride (2 mg/kg iv). Infusion of BMI into the PVN increased mean arterial pressure by 17 +/- 2 mmHg, and heart rate rose by 91 +/- 8 beats/min. Cardiac index increased 17 +/- 3%, whereas total peripheral resistance index was not altered significantly. After metoprolol treatment, the mean arterial pressure response to BMI was similar to control (16 +/- 2 mmHg), but the tachycardia was reduced significantly (10 +/- 4 beats/min). In addition, the blood flow response was changed qualitatively. Total peripheral resistance increased 13 +/- 3%, whereas the cardiac index response was abolished (1 +/- 2%). After prazosin treatment, BMI administration into the PVN failed to increase arterial pressure (-1 +/- 4 mmHg). Nevertheless, the BMI infusion was associated with significant hemodynamic effects. Total peripheral resistance index decreased (-24 +/- 6%), whereas cardiac index and stroke volume index increased 34 +/- 8 and 17 +/- 5%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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